1. Field of the Invention
The present invention relates generally to the field of control arrangements and more particularly to a changeover control arrangement for projection apparatus to allow the alternate energizing of two identical, interconnected projection apparatus.
2. Description of the Prior Art
Various types of control arrangements have been proposed to control the changeover or alternate operation of two interconnected projection apparatus especially in the environment of multi-reel film presentations. At a predetermined point near the end of a film reel, the operator actuates a changeover control to de-energize operation of the projection apparatus projecting the present reel and to energize operation of the second projection apparatus to begin presentation of the next film reel in the multi-reel presentation.
Typically, the changeover control arrangements of the prior art require complex interconnections of the two projection apparatus and interconnection of the electrical systems of the projection apparatus. This interconnection can lead to the interconnected projection apparatus exposing an operator to approximately double the power line source voltage between the two projection apparatus. For example, ground loops in the projection apparatus can be responsible for this condition. Where high intensity projection apparatus is utilized, the problem is more serious due to the presence of 200 to 500 volt potentials between the two projection apparatus.
Further, the changeover control arrangements of the prior art require elaborate electrical interconnections of the two control projection apparatus and complex changeover control circuitry. For example, multiple pole or multiple level switches are required that control electrically interconnected latching and holding relays.
Changeover control arrangements of this general type are disposed for example in U.S. Pat. No. 2,440,184 which issued to J. D. Phyfe on Apr. 20, 1948; U.S. Pat. No. 2,676,272 which issued to J. F. Byrd et al on Apr. 20, 1954; U.S. Pat. No. 2,722,570 which issued to J. F. Byrd et al on Nov. 1, 1955; U.S. Pat. No. 2,774,824 which issued to J. F. Byrd et al on Dec. 18, 1956; U.S. Pat. Nos. 2,542,188 and 2,542,189 which issued to J. T. Gates on Feb. 20, 1951; U.S. Pat. Nos. 2,138,478 and 2,138,479 which issued to F. Pedatella on Nov. 29, 1938; U.S. Pat. No. 2,011,919 which issued to J. Tavani on Aug. 20, 1935; U.S. Pat. No. 1,980,167 which issued to I. H. Crabtree on Nov. 13, 1934; U.S. Pat. No. 1,769,772 which issued to H. C. Cornair on July 1, 1930; U.S. Pat. No. 1,888,276 which issued to A. Loehr, Jr., et al on Nov. 22, 1932; U.S. Pat. No. 1,930,581 which issued to W. W. Blakesley on Oct. 17, 1933; and U.S. Pat. No. 2,002,351 which issued to F. H. Owens on May 21, 1935.
While the various changeover arrangements of the prior art are generally suitable for their intended use, for safety precautions and system simplicity, it would be desirable to have a changeover control system providing complete isolation of two projection apparatus interconnected for changeover operations while utilizing a simple changeover control switch and a minimum number of additional components.